This invention relates, in general, to an apparatus for perforating a subterranean wellbore using shaped charges and, in particular, to a low debris shaped charge perforating apparatus that utilizes contoured recesses in the charge carrier that reduce the size of the holes made in the charge carrier upon detonation of the shaped charges thus enhancing debris containment.
Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation with a shape charge perforating apparatus, as an example.
After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.
Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, one or more charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or the like. Once the charge carriers are properly positioned in the wellbore such that shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a Jet that blasts through a scallop or recess in the carrier. Each jet creates a hydraulic opening through the casing and the cement and enters the formation forming a perforation.
When the shaped charges are detonated, numerous metal fragments are created due to, among other things, the disintegration of the metal casings of the shaped charges. These fragments often fall out or are blown out of the holes created in the carrier. As such, these fragments become debris that is left behind in the wellbore. It has been found that this debris can obstruct the passage of tools through the casing during subsequent operations. This is particularly problematic in the long production zones that are perforated in horizontal wells as the debris simply piles up on the lower side of such wells.
A need has therefore arisen for an apparatus and method that reduce the likelihood that debris will be left in the well following perforation of the formation. A need has also arisen for such an apparatus and method that will contain the fragments created when the shaped charges are detonated. Further, a need has arisen for such an apparatus and method that will enhance the performance of the shaped charges in perforating the formation.
The present invention disclosed herein comprises a shaped charge perforating apparatus and a method for perforating a subterranean formation using a shaped charge perforating apparatus that reduce the likelihood that debris will be left in a well following perforation of a formation. The shaped charge perforating apparatus of the present invention achieves this result by containing the fragments created when the shaped charges are detonated. In addition, the shaped charge perforating apparatus of the present invention enhances the performance of the shaped charges in perforating the formation.
The shaped charge perforating apparatus of the present invention comprises a support member having a plurality of shaped charge mounting locations each of which receive a shaped charge therein. The shaped charges each have an initiation end and a discharge end. The initiation ends of the shaped charges are each coupled to a detonator cord. The shaped charges are placed within an elongated and generally tubular carrier. The carrier has a plurality of recesses that are spaced on the exterior surface thereof and have contoured bottom surfaces. Each of the recesses is axially and radially aligned with the discharge end of one of the shaped charges such that the jet formed upon the initiation of each shaped charge will penetrate the carrier through a recess.
In one embodiment of the present invention, the contoured bottom surface of the recesses is formed such that the center depth of the recess in the carrier is greater than a perimeter depth of the recess. For example, the center depth of the recess may be greater than the perimeter depth of the recess at a point on the perimeter of the recess that is displaced from the center of the recess in a longitudinal direction. Alternatively or additionally, the center depth of the recess may be greater than the perimeter depth of the recess at a point on the perimeter of the recess that is displaced from the center of the recess in a circumferential direction.
In another embodiment of the present invention, the contoured bottom surface of the recesses is formed such that the recesses have a flat bottom portion proximate the center of the recesses and an angular bottom portion extending from the flat bottom portion to the perimeter of the recesses. In this embodiment, the angular bottom portion may have an angle of between about 10 and 40 degrees and may preferably have an angle of between about 15 and 25 degrees.
In one embodiment of the present invention, the contoured bottom surface of the recesses is formed such that the angular bottom portion extends from the flat bottom portion of the recess to the exterior surface of the carrier. In another embodiment of the present invention, the contoured bottom surface of the recesses is formed such that the angular bottom portion of the recess extends from the flat bottom portion of the recess to a sidewall section of the recess at a location offset from the exterior surface of the carrier by a depth.
The method for perforating a subterranean well of the present invention comprises running a shaped charge perforating apparatus of the present invention downhole, operating the shaped charge perforating apparatus and discharging jets formed from the shaped charges through respective contoured bottom surfaces of recesses in the shaped charge carrier. In such a method, the recesses have a center depth that is greater than a perimeter depth, either in the longitudinal direction from the center, the circumferential direction from the center or both. The recesses may have a flat bottom portion proximate the center of the recesses and an angular bottom portion extending from the flat bottom portion to the perimeter of the recesses. The angular bottom portion of the recesses may extend from the flat bottom portion of the recesses to the exterior surface of the carrier or may intersect the sidewall of the recesses at the perimeter of the recesses. In all such configurations, using the method of the present invention to discharge jets formed from the shaped charges through the respective contoured bottom surfaces minimizes the size of openings created through the carrier by the discharge of the jets and prevents peeling of the recesses in the longitudinal direction.